In a packet-switched network, each entity that engages in transmission of packets could be configured with a maximum transmission unit (MTU), defining a maximum allowed packet length for packets transmitted by the entity. The MTU could be defined in terms of the entire datagram output by the entity, including both header and payload, or in terms of the payload alone, among other possibilities.
In accordance with its MTU, when the entity is going output a packet, the entity could determine whether the packet's length exceeds the entity's MTU, and if so, the entity could fragment the packet into multiple parts for output as separate packets. Unfortunately, however, such fragmentation is undesirable, as routing the additional packets could burden the entity and the network, and as issues could arise with reassembly of the fragments at a receiving end, which could lead to required retransmissions and other burdens.